Can you help me understand why C is not correct?
I liked that you've clearly stated the conclusion & premises. You've also tried to apply negation which is an important tool for assumption question. However, I somehow feel that you should give this argument a second read. There are some points which you seem to have missed. I'm sure a re-read would surely help!
To me, the statement seems to conclude that because demand of natural gas (which can be produced in Siduria) is increasing, export of oil (which is mainly from export) will decline
We know that the production of natural gas each year exceeds its demand. I couldn't understand how you've related demand of natural gas with export of oil. Could you please elaborate on this? The argument looks for an option that supports the conclusion that Siduria's reliance on foreign sources for fuel will decline, which means Siduria's import
of fuel would decline.
Conclusion: Reliance on foreign sources for Siduria will decline
Premise: Siduria's demand in natural gas is increasing
Premise: Siduria makes a lot of natural gas
You seem to have missed the conditional structure of the conclusion and that might have led to the fundamental gap in your understanding of this question.
Conclusion: Note the conclusion presents a condition. If X, then Y. If these trends in fuel production and usage continue, therefore, Sidurian reliance on foreign sources for fuel should decline soon.
1) Implementation of a program to convert heating systems from oil to natural gas.
2) Production of natural gas is more than its use each year
3) Oil production in Sidurian oil fields is increasing at a steady pace.
As the conclusion depends on the continuation of trends in fuel production and usage, first we need to understand these trends.
Natural gas: Production of natural gas > its use
As the requirement of natural gas is less than its production, the continuation of this trend is likely to reduce the reliance on foreign sources for natural gas.
As for oil, we know that oil production is increasing at a steady pace; however, unlike the requirement of natural gas, the requirement of oil is not known to us.
If the rate of increase of requirement of oil exceeds or is same as the rate of increase of production of oil, it’s unlikely that Siduria's reliance on foreign sources for fuel will decline soon.
Thus the argument underlies the assumption that
The rate of increase of requirement of oil is lower than the rate of increase of production of oil.
If, for example, the demand of alternative energy, such as bioenergy that might not be able to be produced in Siduria, significantly increases in Siduria, then Siduria will not lower its reliance of foreign source. To me, C is also a pretty solid assumption the author has. I totally agree A is also assumed, but author seems to assume C as well.
If we negate option C, we get:
At least one fuel other than natural gas is expected to be used as a replacement for oil in Siduria.
If I take your example, it means that bioenergy is expected to be used as a replacement of oil. This implies that requirement of oil may decline. Thus, the conclusion doesn't fall apart.
Note: we cannot add information about demand and production of bioenergy. We need to observe the impact of the option in its given form.
Hope this helps!